<!DOCTYPE html>
<html>
<head>
	<title>变量提升</title>
</head>
<body>
<script type="text/javascript">
	
	console.log(a);		// undefined
	var a = 123;


	// 变量提升过程
	/*
		1. var a;
		2. console.log(a);	// undefined
		3. a = 123;
	*/

</script>
</body>
</html>